Urban agriculture systems, such as rooftop greenhouses, are attractive alternatives for mitigating the impacts of the extensive food supply chains that currently feed cities. In this study, we study ...the opportunity that nutrient recirculation offers to improve the environmental performance of agricultural systems. In particular, we analyze the environmental burdens of a hydroponic closed-loop production system that recovers nutrients and reduces water demand by recirculating the irrigation water leaching from the substrate bags along with nutrients that have not been assimilated by the plant. The closed-loop system is compared to a linear system in which there is no nutrient or water recovery. Based on two green bean crop cycles in a Mediterranean rooftop greenhouse, we analyze the yield, climatic variables and water and nutrient balances, and apply life cycle assessment (LCA) to study the environmental impacts.
The results of this study indicate that closed-loop systems save daily 40% of irrigation water and between 35 and 54% of nutrients. Moreover, leachate reuse leads to reduced eutrophication impacts, but it can entail nutrient deficiencies. However, implementing a closed-loop system requires additional infrastructure causing larger impacts than linear systems in terms of global warming and fossil resource scarcity. The results of the LCA were highly sensitive to the yield, the crop production period and the meteorological conditions. Based on these results, we design improved scenarios, providing recommendations for reducing the impacts of closed-loop systems for more sustainable cities.
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•Closed systems presented 40% in daily water savings.•Large savings were obtained in closed systems in eutrophication impacts.•High sensitivity was found related to yield, climatic conditions and crop length.•High impacts in closed systems came from the materials required, mainly benches.•Room for improvement exists for closed systems.
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•The water and nutrient dynamics of a hydroponic crop were assessed.•Most nutrients are drained with the leachates (51% in average).•5% of calcium, 6% of nitrogen and 7% of phosphorus ...are retained in the substrate.•Future studies in hydroponic crops should consider the retention in the substrate.•The balance of the nutrients obtained is more complete than in previous studies.
Global food production systems generate impacts such as eutrophication, caused by nutrient run-off from agricultural exploitations and exacerbated by climate change. Hydroponic cultivation methods are common in Mediterranean areas, although there is a gap in the literature with regard to their study. This study aims to fill that gap, by assessing nutrient flows in hydroponic crops.
The results showed that most of the nutrients were drained with the leachates (51% on average), a figure which could be lower, if the nutrient supply were adjusted to the needs of the plants or if (closed hydroponic) nutrient recirculation were implemented, without compromising the nutrient uptake of the plant. Moreover, the study revealed that a significant quantity of nutrients was retained in the substrate (perlite) during the crop, reaching average values of 5% of incoming calcium, 6% of nitrogen, and 7% of phosphorus. In the case of phosphorus and calcium, a regression model is presented for the estimation of their retention in hydroponic crops.
Although further studies will be needed to confirm the above trends, the study makes a significant contribution to understanding the metabolism of nutrients in hydroponic crops and to finer adjustments of the nutrient balance.
Vertical farming is emerging as an effective measure to grow food in buildings and can increase food production in urban areas in a more sustainable manner. This study presents a comprehensive ...environmental assessment of food production in an integrated rooftop greenhouse (i-RTG) – an innovative vertical farm consisting of a rooftop greenhouse connected to a building – and considers rainwater, residual heat (energy), residual air (CO2) and food from an industrial ecology perspective. This synergistic connection preserves resources and improves conditions in the greenhouse and the building. The goal of the study is to show the feasibility of the system and to calculate the environmental impacts from its whole life cycle, from infrastructure to end of life, by comparing these impacts with those of conventional production. The results show that the system is feasible and produced 30.2 kg/m2 of tomato over 15.5 months. The synergy with the building allows the cultivation of winter-fall crops without supplying heating and maintained an average temperature 8 °C higher than that outdoors. Moreover, rainwater was used to irrigate the crops, reducing consumption from the water supply network by 80–90%. The environmental assessment showed that the operation of the i-RTG has more impacts than the infrastructure (structure of the greenhouse, rainwater harvesting system and equipment) due to the use of fertilisers, which account for 25% of the impacts in four of the six impact categories studied. Regarding the infrastructure, the greenhouse structure and rainwater harvesting system of the building have substantial environmental impacts (over 30% in four of the six impact categories). Comparison with a conventional greenhouse demonstrates that the i-RTG has a better environmental performance, showing between 50 and 75% lower impacts in five of the six impact categories (for instance, 0.58 kg of CO2 equivalent per kg of tomato vs. 1.7 kg), mainly due to the reduced packaging and transport requirements. From this study, it was concluded that optimisation of the amount of infrastructure material and management of the operation could lead to even better environmental performance in future i-RTG projects.
•The i-RTG is an innovative system for food production in cities.•The system can grow 19.6 kg of tomato/m2·year (1653 kg/year for the case study).•Tomato production in the i-RTG holds 66% lower GHG emissions than conventional.•The symbiosis with the building provides 80–90% of the water demand.•The application of i-RTG at larger scale would improve its efficiency.
There is great potential to reduce the environmental impact of the building sector, which is now an area of immense importance, through the optimisation of construction materials and components. This ...study assesses both the design and the construction of Concrete Deep Foundations (CDFs), which are widely used in construction, from an environmental perspective considering the following variables: (i) grade of prefabrication, i.e., fully cast in situ, partly prefabricated, and fully prefabricated; (ii) compressive strength of cast-in-situ concrete; and (iii) building design codes, i.e., current Spanish codes (EHE-08 and CTE), Eurocode with the Spanish annexes, and Eurocode with the United Kingdom annexes. In addition, the results of Dynamic Load Tests (DLTs) and the economic cost of several CDFs are evaluated. Geotechnical and structural designs of CDFs are carried out along with their life-cycle assessment. Some of the main findings include: (i) partially and fully prefabricated CDFs and conducting DLTs reduced the environmental impact in most categories (by up to 44% for global warming emissions) compared to the fully cast-in-situ CDFs, although they were 12–37% more expensive; (ii) changing the compressive strength of the concrete (in piles and cap) in fully cast-in-situ CDFs from 25 to 35 MPa reduced the environmental impact by up to 14–17% in all categories and economic costs by up to 12%; and, (iii) CDFs with bored piles resulted in the lowest environmental burden when designed with Eurocode and UK annexes (11–31% less impact), as did CDFs with driven piles designed with current Spanish codes (11–18% less impact). The study variables and sensitivity analysis showed a significant effect on the results and should be considered in future construction, research, and building codes.
•The prefabrication of Concrete Deep Foundations (CDFs) reduces environmental impact and increases the economic cost.•Increasing the compressive strength of concrete reduces environmental impact and cost.•Conducting Dynamic Load Tests on driven piles reduces environmental impact and cost.•CDFs with bored piles are environmentally better designed with Eurocode with UK annexes.•CDFs with driven piles are environmentally better designed with current Spanish codes.
Purpose
The methods for assessing the impact of using abiotic resources in life cycle assessment (LCA) have always been heavily debated. One of the main reasons for this is the lack of a common ...understanding of the problem related to resource use. This article reports the results of an effort to reach such common understanding between different stakeholder groups and the LCA community. For this, a top-down approach was applied.
Methods
To guide the process, a four-level top-down framework was used to (1) demarcate the problem that needs to be assessed, (2) translate this into a modeling concept, (3) derive mathematical equations and fill these with data necessary to calculate the characterization factors, and (4) align the system boundaries and assumptions that are made in the life cycle impact assessment (LCIA) model and the life cycle inventory (LCI) model.
Results
We started from the following
definition of the problem
of using resources: the decrease of accessibility on a global level of primary and/or secondary elements over the very long term or short term due to the
net
result of compromising actions. The
system model
distinguishes accessible and inaccessible stocks in both the environment and the technosphere. Human actions can compromise the accessible stock through environmental dissipation, technosphere hibernation, and occupation in use or through exploration. As a
basis for impact assessment
, we propose two parameters: the global change in accessible stock as a net result of the compromising actions and the global amount of the accessible stock. We propose three impact categories for the use of elements: environmental dissipation, technosphere hibernation, and occupation in use, with associated characterization equations for two different time horizons. Finally, preliminary characterization factors are derived and applied in a simple illustrative case study for environmental dissipation.
Conclusions
Due to data constraints, at this moment, only characterization factors for “dissipation to the environment” over a very-long-term time horizon could be elaborated. The case study shows that the calculation of impact scores might be hampered by insufficient LCI data. Most presently available LCI databases are far from complete in registering the flows necessary to assess the impacts on the accessibility of elements. While applying the framework, various choices are made that could plausibly be made differently. We invite our peers to also use this top-down framework when challenging our choices and elaborate that into a consistent set of choices and assumptions when developing LCIA methods.
Urban agriculture has emerged as an alternative to conventional rural agriculture seeking to foster a sustainable circular economy in cities. When considering the feasibility of urban agriculture and ...planning for the future of food production and energy, it is important to understand the relationships between energy flows throughout the system, identify their strengths and weaknesses, and make suggestions to optimize the system. To address this need, we analyzed the energy flows for growing tomatoes at a rooftop greenhouse (RTG). We used life cycle assessment (LCA) to identify the flows within the supply chain. We further analyzed these flows using ecological network analysis (ENA), which allowed a comparison of the industrial system to natural systems. Going beyond LCA, ENA also allowed us to focus more on the relationships between components. Similar to existing ENA studies on urban metabolism, our results showed that the RTG does not mimic the perfect pyramidal structure found in natural ecosystems due to the system's dependency on fossil fuels throughout the supply chain and each industry's significant impact on wasted energy. However, it was discovered that the RTG has strong foundational relationships in its industries, demonstrating overall positive utility; this foundation can be improved by using more renewable energy and increasing the recycling rates throughout the supply chain, which will in turn improve the hierarchy of energy flows and overall energy consumption performance of the system.
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•The energy-food nexus in urban agriculture was studied through interindustry flows.•We conducted an ecological network analysis using life cycle data.•An integrated rooftop greenhouse was assessed as an innovative case study.•The energy trophic structure does not mimic efficient natural metabolic systems.•Energy dissipation could be improved through renewable energy.
Purpose
Rooftop greenhouses (RTGs) are agricultural systems that can improve the food supply chain by producing vegetables in unused urban spaces. However, to date, environmental assessments of RTGs ...have only focused on specific crops, without considering the impacts resulting from seasonality, combinations of crops and nonoperational time. We analyze vegetable production in an RTG over 4 years to determine the crop combinations that minimize yearly environmental impacts while diversifying food supply.
Methods
The system under study consists of an integrated RTG (i-RTG) with a hydroponic system in Barcelona, in the Mediterranean region. By using life cycle assessment (LCA), we evaluate the environmental performance of 25 different crop cycles and 7 species cultivated during the period 2015–2018. Three functional units are used: 1 kg of edible fresh production, 1 unit of economic value (€) in the wholesale market and 1 kcal of nutritional value. The system boundaries consider two subsystems: infrastructure (greenhouse structure, rainwater harvesting system and auxiliary equipment) and operation (fertilizers and their emissions into water and substrate). In addition, we perform an eco-efficiency analysis, considering the carbon footprint of the crop cycles and their value at the wholesale market during their harvesting periods.
Results and discussion
Spring tomato cycles exert the lowest impacts in all categories, considering all three functional units, due to the high yields obtained. In contrast, spinach and arugula have the highest impacts. Regarding relative impact, the greenhouse structure presented a large impact, while fertilizer production had notable relative contributions in tomato cycles. Moreover, nitrogen and phosphorus emissions from fertigation are the main causes of freshwater and marine eutrophication. By combining the most eco-efficient cycles, we can see that growing two consecutive tomato cycles is the best alternative with the functional unit of yield (0.49 kg CO
2
eq./kg), whereas a long spring tomato cycle combined with bean and lettuce cycles in the autumn/winter is the best scenario when using market (0.70 kg CO
2
eq./€) and nutritional value (3.18·10
−3
kg CO
2
/ kcal).
Conclusions
This study shows that increasing the diversity of the system leads to better environmental performance of greenhouse urban agriculture if suitable crops are selected for the autumn/winter season. The functional unit involving the economic value and the eco-efficiency analysis are useful to demonstrate the capability of the growing system to produce added-value vegetables under harsher conditions while categorizing and classifying the crops to select the most suitable combinations based on economic and environmental parameters.
Assessing the sustainability of waste management systems (WMSs) is key to reduce the impacts incurred by human activities. The article presents the development of an operational sustainability ...framework for the assessment of WMSs involving stakeholders and experts from different fields. The operational framework presented achieves comprehensiveness by including multidisciplinary impacts (environmental, social, and economic impacts), accounting for spatial differentiation regarding the occurrence and magnitude of the impacts (local to global) and complementing well-established methods in life cycle assessment (LCA) with local impact assessment methods. In this respect, the assessment of social local impacts (e.g., Odour, Landscape Disamenities), which has so far received little attention in the literature, has been included. The procedure for the definition of the operational framework is described in detail, including the selection of the impact categories and associated indicators. Finally, an aggregation method was defined considering the perception of stakeholders, allowing for aggregating the impact in five areas of protection (Prosperity, Human Well-Being, Human Health, Ecosystem Health and Natural Resources).
•Two stationary energy storage systems are compared for renewable energy.•Photovoltaic and wind energy are assessed as renewable source for grid application.•Environmental impacts are quantified from ...production to end-of-life.•Use phase and end-of-life contribute significantly to overall environmental impact.•Vanadium redox flow battery-based system results in lower environmental impact.
Renewable energy has become an important alternative to fossil energy, as it is associated with lower greenhouse gas emissions. However, the intermittent characteristic of renewables urges for energy storage systems, which play an important role in matching the supply and demand of renewable-based electricity. The life cycle of these storage systems results in environmental burdens, which are investigated in this study, focusing on lithium-ion and vanadium flow batteries for renewable energy (solar and wind) storage for grid applications. The impacts are assessed through a life cycle assessment covering the batteries supply phase, their use and end-of-life, with experimental data from test set-ups. The battery composition is investigated in detail as a factor for the final impacts, by comparing two types of cathodes for the lithium-ion battery and the use of recycled electrolyte for the vanadium flow battery. Results indicate that the vanadium-based storage system results in overall lower impacts when manufactured with 100% fresh raw materials, but the impacts are significantly lowered if 50% recycled electrolyte is used, with up to 45.2% lower acidification and 11.1% lower global warming potential. The new lithium-ion battery cathode chemistry results in overall higher impacts, with 41.7% more particulate matter and 52.2% more acidification.
•Multi-fold local & global data collected and processed into a comprehensive framework•Anaerobic digestion with effective nutrient recovery appears the best option•All alternative strategies to ...incineration increase food waste management costs•Aggregation makes findings accessible to the widest possible audience and stakeholder•The study informs stakeholders and authorities on the consequences of their options
Food waste represents the largest fraction of the municipal solid waste generated in Europe and its management is associated to suboptimal performance in environmental, health, and social dimensions. By processing detailed multi-fold local data as part of a comprehensive and broadly understandable sustainability framework, this study quantifies the environmental and socio-economic impacts of household food waste management in the Amsterdam Metropolitan Area based on priorities set by local stakeholders. Five alternative short-term management options have been assessed against the current system, relying on poor separate collection and incineration. Four options involve separate collection of food waste followed by biological treatments (home/centralised composting and anaerobic digestion) while one involves a mix of separate collection and centralised mechanical-biological treatment followed by anaerobic digestion. Among these, separate collection followed by anaerobic digestion coupled with effective nutrient and energy recovery is, according to our findings, the preferred option to improve the sustainability of the current system in all dimensions considered, except for the economic pillar due to the collection costs. Home and centralised composting as well as mechanical-biological treatment are associated to more adverse impacts based on our findings. The study informs local stakeholders and authorities on the potential consequences of their options, thereby allowing them to make sound choices for a future waste and circular economy strategy.
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